(1) Field of the Invention
This invention relates to the novel disodium salt of ethoxylated rosin half esters of sulfosuccinic acid prepared from 1-5 mole rosin ethoxylates which are useful as foam stabilizers in a latex composition. This invention also relates to styrene-butadiene and carboxylated styrene-butadiene latex compositions containing the foam stabilizers and a process for preparing said latex compositions which can be formed into a non-gelling, heat-curable solid foam suitable for use as a foam carpet backing.
(2) Description of the Prior Art
The conversion of an aqueous emulsion or dispersion of a polymer into a wet foam is made possible because of the fact that the polymer is dispersed in a continuous aqueous phase so that the emulsion is highly fluid and therefore can be foamed. Foaming of an emulsion, to convert the emulsion into a wet foam consisiting of a mass of bubbles, is performed by subjecting the emulsion to mechanical action, for example by whipping the emulsion or by introducing or generating gas to form bubbles from the emulsion. At the instant when the mechanical foaming action stops, however, the wet foam starts to collapse because the emulsion, consisting of a dispersion of the polymer in a continuous aqueous phase, is still highly fluid.
One way in which a wet foam, formed from an aqueous emulsion of a polymer, is converted into a solid cellular material so as to prevent the foam from collapsing has consisted in causing gelling of the aqueous emulsion of which the wet foam is composed. Thus, in the case of polymers which form a gelatinous, stiff continuous phase upon gelling of the aqueous emulsion, employing a gelling agent prevents the collapse of a wet foam. Such techniques are disclosed in U.S. Pat., Nos. 2,706,183 and 3,215,647. The commonly used gelling agents are ammonium acetate and sodium silico-fluoride, or blends of these two ingredients, which are incorporated into the foam after frothing by the use of a blender. The level of gelling agent requires careful, often critical, control. Too little results in heavy skin formation, inferior structure or even gross collapse, while too much results in surface imperfections.
A typical gel foam formulation for foam backing of tufted carpets is shown in Table I.
______________________________________ TYPICAL GEL FOAM FORMULATION Parts Dry Weight ______________________________________ SBR Latex 100.0 Potassium Oleate 3.0 Sulphur 2.0 Antioxidant 1.0 Pigment as required Ammonia 0.5 Filler (Whiting or Clay) 75.0 Zinc Oxide 5.0 Ammonium Acetate 3.0 ______________________________________ Weight Applied = 20-40 ozs/yd.sup.2 Total Solids = 65-70%
Another, more recently developed, method of preventing collapse of a wet foam does not include a gelling agent, hence the name "no-gelled" foam. The system works the opposite way to all other latex foam systems in that a surfactant is added which promotes excessive colloid stability, and the stability is so high that the addition of gelling agents would have little or no effect on colloid stability. To produce the final foam from such a system the water is removed, thus separating the latex particles. Once this has been done, the particles can coalesce to form a coherent mass. This system has rapidly grown in importance, largely because the system is much cheaper than the original gelled foam system.
A typical no-gel foam formulation for foam backing of tufted carpets is shown in Table II.
TABLE II ______________________________________ TYPICAL NO-GEL FOAM FORMULATION Parts Dry Weight ______________________________________ SBR Latex 100.0 Disodium N-octadecyl Sulfosuccinamate 4.0 Potassium Hydroxide 0.2 Sodium Hexametaphosphate 0.5 Pigment as required Filler (Whiting and/or Alumina) 150.0 Polyacrylate Thickener 5.9 ______________________________________ Weight Applied = 16-40 ozs/yd.sup.2 (dry) Total Solids = 73-78%
The purpose of the filler, obviously, is to extend the foaming material with a less expensive additive; and it can be added up to 200 parts per one hundred parts of latex without seriously detracting from the foaming properties. Whether alumina is employed as filler, either alone or in conjunction with calcium carbonate (whiting), normally depends upon the degree of fire retardancy desired.
Known foam stabilizers include disodium N-octadecyl sulfosuccinate and sodium lauryl sulfate (U.S. Pat. No. Re. 27,366 and U.S. Pat. No. 3,740,357). U.S. Pat. No. 3,823,104 discloses blends of certain saturated or unsaturated fatty alcohols and fatty acid amidos; and U.S. Pat. No. 3,856,722 discloses alkali metal salts of liquid, water-soluble higher aliphatic fatty acid ethanolamide sulfosuccinate as latex foam stabilizers. U.S. Pat. No. 3,948,822 proposes disodium N-octadecyl sulfosuccinate in combination with sodium formaldehyde sulfoxylate as an emulsifier in a no-gel system. The foam stabilizer is normally employed in an amount equal to from 1.5% to 15% of the weight of the polymer in the emulsion.
For many years the production of foam rubber backed tufted carpet has been accomplished by an aqueous latex method. This method involves preparing a tufted structure by stitching a primary backing material with yarn in such a manner as to form on the top surface of the material a pile composed of numerous closely spaced erect loops of fiber bundles, i.e., tufts of yarn. If desired, the loops can be cut. After forming the tufted structure, the bottom surface thereof is anchor-coated with a latex containing a polymer binder such as a styrene-butadiene copolymer, dried with infra red heat, and then spread with foam, which is applied via a plastic or stainless steel hose mounted on a trolley, which traverses across the carpet width. Stainless steel deckles are located on the carpet edges to maintain the foam within the carpet width. The carpet is kept under tension in order to avoid creasing and to obtain a flat foam surface. Immediately after the spreading point, the foam is passed under infrareds which gel the foam, or, in the case of no-gelled foams, merely skin the surface. The carpet is then carried through an oven, in order to drive off the moisture and cure the foam.
Carpet is passed through the oven usually in the pile down position, and modern systems incorporate a "split temperature zone", the top temperature being set to cure the foam and the bottom set in relation to the pile content. Drying and curing is usually carried out in ovens between 70 and 180 feet in length with temperatures ranging from 130.degree. C. to 160.degree. C. The cure or drying time of the foam is dependent basically on the wet foam density and the weight applied, as well as the efficiency and the temperature of the oven. On completion of the cure, the foam-backed carpet is cooled, batched and then packaged. A cooling section helps to minimize shrinkage of the carpet.
In the preparation and application of foamed rubber backings for carpets for sound damping, to provide walking comfort and to prevent the carpet from slipping, the most commonly employed foam stabilizer/agent/emulsifier is disodium N-octadecyl (or disodium tallow amine) sulfosuccinamate. It is substantially water insoluble, paste like and difficult to handle. Its paste-like consistency limits somewhat its use with higher solids containing latex formulations. Unfortunately, the overall styrene-butadiene resin containing as the emulsifier, disodium tallow amine sulfosuccinamate, is not entirely satisfactory for the reason that its preparation is difficult to perform, due to the paste-like nature of the emulsifier and the composition possesses a relatively high foam density requiring large quantities of composition to cover a given area of carpet. Finally, the tallow amine-derived foaming agent represents a significant processing cost considering its proportion in the formulation. As foam rubber, mainly styrene-butadiene rubber latex, accounts for approximately 90% of the yardage of integral cushioned carpet, and with the use of foamed rubber latex backing for carpets increasing, it would be advantageous to provide a more economical foaming agent and a latex composition containing same which exhibit a low foam density, requiring the use of lower quantities of composition to cover a given area, as well as improved processing and handling characteristics.
It is, therefore, a principal object of the invention to provide a novel, relatively inexpensive foaming agent which is in a liquid, easily handleable form. It is a further object to provide a latex composition suitable as a foamed rubber backing for carpets possessing a relatively low foam density and stability to allow for substantial cost savings and complete cure without collapse of the backing. Other objects and advantages will become apparent in the following discussion.